1. Technical Field
The present invention is directed generally to the treatment or prevention of addictions using PPARγ agonists, alone or in combination with other therapeutic agents.
2. Description of the Related Art
The World Health Organization (WHO) defines substance addiction as using a substance repeatedly, despite knowing and experiencing harmful effects. Substance addiction is a chronic, relapsing disease characterized by a loss of control over drug use, compulsive drug seeking and craving for a substance, use that persists despite negative consequences, and physical and/or psychological dependence on the substance. Substance addiction typically follows a course of tolerance, withdrawal, compulsive drug taking behaviour, drug seeking behaviour, and relapse. Substance abuse and addiction are public health issues with significant social and economic impact on both the addict and society by playing a major role in violent crime and the spread of infectious diseases. Addictive substances include alcohol, caffeine, nicotine, cannabis (marijuana) and cannabis derivatives, opiates and other morphine-like opioid agonists such as heroin, phencyclidine and phencyclidine-like compounds, sedative ipnotics such as benzodiazepines and barbiturates and psychostimulants such as cocaine, amphetamines and amphetamine-related drugs such as dextroamphetamine and methylamphetamine.
Alcohol is one of the most commonly abused substances at a global level. Additionally, alcoholism leads to serious liver and cardiovascular disease and generates dependence resulting in severe mental disorders, social problems and adverse consequences including the division of families, tragic accidents and the reduction of work performance. According to the WHO, alcohol consumption is responsible for 20-30% of oesophageal and liver cancer, liver cirrhosis, homicides, epilepsy, and motor vehicle accidents world wide. Globally, alcohol abuse leads to about 1.8 million deaths per year. Compulsive behaviour towards the consumption of alcohol is a core symptom of the disorder. In recent years several approaches have been investigated to help alcoholic patients to not only control alcohol drinking but also alcohol cravings and relapse (Monti et al., 1993; Volpicelli et al. 1992; O'Brien et al. 1997).
Medications such as naltrexone, acamprosate, ondansetron, disulfiram, gamma hydroxybutyrate (GHB), and topiramate tested for their potential therapeutic effect on alcohol abuse belong to several classes (Volpicelli et al. 1992; O'Brien et al. 1997). Few of these pharmacotherapeutics, such as naltrexone, acamprosate, and disulfiram, have been proven to be of a certain utility and approved for the treatment of alcoholism. Among these medications, the non-selective opioid antagonist naltrexone is currently considered the pharmacological gold standard. However, despite some promising results none of these medications, including naltrexone, is of sufficient efficacy in alcoholism and prognosis remains poor.
Nicotine is one of the most widely used addictive drugs, and nicotine abuse is the most common form of substance abuse. The WHO estimates that there are 1.25 billion smokers worldwide, representing one third of the global population over the age of 15. The WHO further estimates that 5 million deaths occur each year as a direct result of tobacco use, making nicotine abuse the largest single preventable cause of death worldwide. In industrialized countries, 70-90% of lung cancer, 56-80% of chronic respiratory disease, and 22% of cardiovascular disease instances are attributed to nicotine addiction. Cigarette smoking is associated with 430,000 deaths a year in the US alone and is estimated to cost the nation 80 billion dollars yearly in health care costs. Tobacco use accounts for one third of all cancers, including cancer of the lung, mouth, pharynx, larynx, esophagus, cervix, kidney, ureter, and bladder. The overall rates of death from cancer are twice as high among smokers as among nonsmokers. Smoking also causes lung diseases such as chronic bronchitis and emphysema; exacerbates asthma symptoms; and increases the risk of heart disease, including stroke, heart attack, vascular disease, and aneurysm. An estimated 20% of the deaths from heart disease are attributable to smoking. Expectant women who smoke are at greater risk than nonsmokers for premature delivery, spontaneous abortion, and infants with decreased birth weight.
Nicotine use results in increased levels of the neurotransmitter dopamine, which activates the reward pathways to regulate feelings of pleasure and to mediate the desire to consume nicotine. Symptoms associated with nicotine withdrawal include craving, irritability, anger, hostility, aggression, fatigue, depression, and cognitive impairment, which lead the abuser to seek more nicotine. Environmental conditioning factors and exposure to psychological stress represent additional factors motivating nicotine use in smokers. Repeated nicotine use results in the development of tolerance, requiring higher doses of nicotine to produce the same initial stimulation.
Most therapies developed for nicotine addiction have shown only moderate success in preventing relapse, leading to a high failure rate in attempts to quit smoking. Treatments include the use of nicotine replacement products, anti-depressants, anti-hypersensitives, and behavioural therapy.
The National Institute on Drug Abuse estimates that 72 million Americans, about one third of the population, have tried marijuana. Acute effects of marijuana use include memory and learning problems, distorted perception, difficulty problem solving, loss of coordination, and increased heart rate. Long term abuse can cause the same respiratory problems observed in tobacco smokers, such as daily cough, phlegm production, increased risk of lung infections, and an increased chance of developing cancer of the head, neck and lungs. Depression, anxiety, and job-related problems have been associated with marijuana use. Long term marijuana use can result in addiction with compulsive use that interferes with daily activities. Cravings and withdrawal symptoms, such as irritability, increased aggression, sleeplessness, and anxiety make it difficult for addicts to stop using marijuana. There are no pharmaceutical treatments available for treating marijuana addiction and relapse.
According to the WHO, an estimated 13 million people abuse opiates world wide, including 9 million heroin addicts. More than 25% of opiate abusers die from suicide, homicide, or an infectious disease, such as HIV and hepatitis, within 10-20 years of becoming addicted. Tolerance and physical dependence can develop within two to three days.
The goals for treatment of opiate addiction, as with other types of substance addictions, are to discontinue the use of the opiate while minimizing painful withdrawal symptoms and preventing relapse. Current treatments involve replacing the addictive drug with a substitution of an opioid receptor agonist or mixed agonist/antagonist. An alternative approach consists of the use of an opioid receptor antagonist to block the effect of the agonist. Antagonists provide no relief from pain or other withdrawal symptoms; rather, they can precipitate withdrawal, and their therapeutic use was associated with increased accidental opioid agonists overdosing and increased lethality. Use of agonists with a lower affinity for the receptors results in the least severe withdrawal symptoms, but it can lead to a dependence on the substitute opiate. Also, many substitution therapies take 3-6 months, allowing time for addicts to stop treatment midway.
Psychostimulants, such as cocaine and amphetamines, cause euphoria, increased alertness, and increased physical capacity in humans. These substances first increase dopamine transmission, but long term drug usage results in a reduction of dopamine activity, leading to dysregulation of the brain reward system and dysporia. The WHO estimates 33 million people around the world abuse amphetamines.
Chronic cocaine abuse can result in hyperstimulation, tachycardia, hypertension, mydriasis, muscle twitching, sleeplessness, extreme nervousness, hallucinations, paranoia, aggressive behaviour, and depression. Cocaine overdose may lead to tremors, convulsions, delirium, and death resulting from heart arrhythmias and cardiovascular failure. Desipramine, amantadine and bromocriptine have been shown to decrease cocaine withdrawal symptoms.
Amphetamine withdrawal symptoms include EEG changes, fatigue, and mental depression. Tolerance develops over time and may be associated with tachycardia, auditory and visual hallucinations, delusions, anxiety reactions, paranoid psychosis, exhaustion, confusion, memory loss, and prolonged depression with suicidal tendencies. Current treatments for amphetamine addiction include phenothiazines, haloperidol, and chlorpromazine for hallucinations, but potential side effects of these drugs include postural hypotension and severe extrapyramidal motor disorders.
In the past, treatment for substance addictions focused on behavioural therapy, but dependence on many of these highly addictive substances is hard to break. In particular, addictions to alcohol, cocaine, and heroin are considered chronic, relapsing disorders. Also, concurrent abuse of multiple substances, such as nicotine, heroin, cocaine and alcohol, is common.
The long-lasting, chronic nature of many addictions and high rates of recidivism present a considerable challenge for the treatment of drug and alcohol addiction, such that understanding of the neurobiological basis of relapse has emerged as a central issue in addiction research. Emotional and environmental factors (conditioning stimuli) were listed among the main causes of relapse. For example, it is known that specific stress conditions such as loss of work and economic difficulties, or stimuli predictive of the presence of alcohol previously associated with its use such as a bottle of the preferred wine and a bar-like environment, may strongly facilitate relapse in detoxified former alcoholics.
Two major theoretical positions exist to explain the persistence of addictive behaviour and vulnerability to relapse associated with drug and alcohol addiction, homoeostatic hypotheses and conditioning hypotheses.
Homeostatic hypotheses relate relapse risk to neuroadaptive changes and disruption of neuroendocrine homeostasis that are thought to underlie anxiety, mood dysregulation and somatic symptoms that accompany acute withdrawal, and that can persist for considerable periods of time during what has been referred to as the “protracted withdrawal” phase. This view, therefore, implicates alleviation of discomfort and negative affect as a motivational basis for relapse.
Conditioning hypotheses are based on observations that relapse is often associated with exposure to drug-related environmental stimuli. This view holds that specific environmental stimuli that have become associated with the rewarding actions of a drug by means of classical conditioning can elicit subjective states that trigger resumption of drug use. The homeostatic and conditioning hypotheses are not mutually exclusive. In fact, homeostatic and conditioning factors are likely to exert additive effects in that exposure to drug-related environmental stimuli may augment vulnerability to relapse conveyed by homeostatic disturbances.
Clearly, there is a need in the art for new methods for treating and preventing addiction and the relapse use of addictive agents. The present invention meets these needs by providing methods and pharmaceutical combinations useful in treating and preventing addiction and recividism.